1. Field of the Invention
The present invention relates to bandpass filter devices and more specifically relates to filter devices having a ladder circuit configuration.
2. Description of the Related Art
To date, surface acoustic wave filter devices having a ladder circuit configuration have been widely used in, for example, bandpass filters of mobile communication devices.
In Japanese Unexamined Patent Application Publication No. 2003-332885, an example of such a filter device is disclosed. In the filter device described in Japanese Unexamined Patent Application Publication No. 2003-332885, a surface acoustic wave filter device is mounted on a chip substrate. The surface acoustic wave filter device includes a piezoelectric substrate and an electrode structure formed on one main surface of the piezoelectric substrate. This electrode structure includes series arm resonators, parallel arm resonators and wiring conductors that electrically connect the series arm resonators and the parallel arm resonators to each other. Electrode lands, which are provided on the surface acoustic wave filter device and the chip substrate, are electrically connected to one another through bonding wires. In addition, surface mount terminal electrodes are formed on an outer surface of a package member in which the chip substrate is included.
To date, various configurations have been proposed for electrically connecting inductances, which are for band adjustment and so forth, to the series arm resonators and the parallel arm resonators in such a filter device having a ladder circuit configuration.
In the filter device described in Japanese Unexamined Patent Application Publication No. 2003-332885, inductances are formed on the piezoelectric substrate of the surface acoustic wave filter device and on a package member on which the surface acoustic wave filter device is mounted, for example, on the chip substrate.
However, in such a filter device, it has been difficult to obtain sufficient out-of-band attenuation.
In addition, it has been difficult to reduce the size of a filter device having a ladder circuit configuration and a structure in which the filter device is mounted on a mounting substrate.